Studies on Forecast of Cool Weather Damage of Rice Growth in Aomori Prefecture

Abstract

In this paper, the characteristics in the regional change of the dependence of rice yield on cool weather conditions in a summer season were investigated on the basis of both the relationship between the rice yield and cool weather conditions and data on the occurrence of low air temperature in the season. The results so obtained may be summarized as follows1. Aomori pref. was found to be divided into five groups from the standpoint of the weather dependence of rice growth (see Table 3). The rice growth in the most sensitive region to the delay-type damage (caused by the delay of the heading due to lower air temperature through the vegetative growth period) was recognized to be also greatly affected by such a lower air temperature in the heading period as it injures the young head of rice.2. Two factors, daily mean air temperature during the growing season of rice and difference in day between the actual heading time and the critical heading time assuring the perfect ripeness of rice grain, were took into consideration for establishing the measure of forecast of the yield from weather conditions. Using the accumulated air temperature for the period from the sowing to the heading (it changes with the variety of rice and the type of nursery bed), the measure was applied to forecast the degree in decrease of rice yield by such weather conditions as experienced in years with cool weather damage of rice growth. The results indicate that the rice yield at 1953 and 1954, in which the cool weather damage was observed in Aomori pref., should become about 96per cent and 93per cent of the mean yield in years with normal weather conditions, respectively, if recent improved techniques were used at these years. The above fact seems to imply that the present techniques in rice growing is valuable to help the stabilization of the yearly variation in rice yield.